One drawback of using a mobile communication device is that the noise around a user of a mobile communication device can vary dramatically as the user travels from place to place. Further, since mobile communication devices are used in such a wide variety of environments, including outdoors, the noise around the user of the mobile communication device can vary even when the user is not traveling from place to place. The surrounding noise can cause several problems. For example, the noise, if loud enough can hinder the user's ability to hear a party on the other end of a call. As a result, mobile communication devices have been designed to include variable gain audio amplifiers, the gain of which can be adjusted based on the surrounding noise level. Thus, if it is determined that the surrounding noise level is too high, then the gain of the audio amplifier can be adjusted, which increases the volume of the audio output so that the user is better able to hear what the other party is saying.
FIG. 1 is a graph depicting an example gain curve for a device that can adjust the volume output by its audio system based on noise level, thereby increasing the Signal-to-Noise-Ratio (SNR) for the user of the audio output. The graph includes an x-axis that indicates noise level and a y-axis that indicates gain. Moving along x-axis, the gain applied to the audio output signal is at an initial level 20 until the noise level reaches a first threshold level 16. At the first threshold level 16, the gain is increased to level 22. As the noise level reaches a second threshold level 18, the gain is increased again from level 22 to level 24. Thus, as the noise level increases, the volume level of the audio output will increase as a result of the increased gain levels applied as each threshold is reached, which will in turn increase the SNR.
Accordingly, due to the increased SNR in noisy conditions, the user of such a device can, in some cases, better hear and understand the output of the audio system even in the face of noise. This is obviously due to the fact that, as the noise surrounding the device increases, the volume output is incrementally increased to counteract the surrounding noise. Depending on the implementation, different threshold noise levels and different gain steps can be used. Additionally, more, or fewer threshold noise levels can be used.
The simple approach to counteracting noise, depicted in FIG. 1, does have drawbacks. For example, the ability of the human ear to hear sound of different frequencies in a noisy environment can vary as noise level increases. In other words, tonal masking, wherein the audibility of one sound is reduced due to the presence of another sound at a close frequency, can cause a person to be able to hear some frequencies better than others. Additionally, the ability of a speaker device to reproduce sound accurately and without distortion can vary as volume is increased. This may limit how much the volume can be increased as the surrounding noise level increases. As a result, the approach depicted in FIG. 1 can be ineffective in many situations.